1. Field of the Invention
The present invention relates generally to apparatus and methods for cementing downhole tubulars into a well bore, and more particularly, the present invention relates to a cementing manifold assembly and method of use.
2. Description of the Related Art
A well-known method of drilling hydrocarbon wells involves disposing a drill bit at the end of a drill string and rotating the drill string from the surface utilizing either a top drive unit or a rotary table set in the drilling rig floor. As drilling continues, progressively smaller diameter tubulars comprising casing and/or liner strings may be installed end-to-end to line the borehole wall. Thus, as the well is drilled deeper, each string is run through and secured to the lower end of the previous string to line the borehole wall. Then the string is cemented into place by flowing cement down the flowbore of the string and up the annulus formed by the string and the borehole wall.
To conduct the cementing operation, typically a cementing manifold is disposed between the top drive unit or rotary table and the drill string. Thus, due to its position in the drilling assembly, the cementing manifold must suspend the weight of the drill pipe, contain pressure, transmit torque, and allow unimpeded rotation of the drill string. When utilizing a top drive unit, a separate inlet is preferably provided to connect the cement lines to the cementing manifold. This allows cement to be discharged through the cementing manifold into the drill string without flowing through the top drive unit.
In operation, the cementing manifold allows fluids, such as drilling mud or cement, to flow therethrough while simultaneously enclosing and protecting from flow, a series of darts and/or spheres that are released on demand and in sequence to perform various operations downhole. Thus, as fluid flows through the cementing manifold, the darts and/or spheres are isolated from the fluid flow until they are ready for release.
Cementing manifolds are available in a variety of configurations, with the most common configuration comprising a single sphere/single dart manifold. The sphere is dropped at a predetermined time during drilling to form a temporary seal or closure of the flowbore of the drill string, for example, or to actuate a downhole tool, such as a liner hanger, in advance of the cementing operation, as for example. Once the cement has been pumped downhole, the dart is dropped to perform another operation, such as wiping cement from the inner wall of a string of downhole tubular members.
Another common cementing manifold comprises a single sphere/double dart configuration. The sphere may be released to actuate a downhole tool, for example, followed by the first dart being launched immediately ahead of the cement, and the second dart being launched immediately following the cement. Thus, the dual darts surround the cement and prevent it from mixing with drilling fluid as the cement is pumped downhole through the drill string. Each dart typically also performs another operation upon reaching the bottom of the drill string, such as latching into a larger dart to wipe cement from the string of downhole tubular members.
Many conventional cementing manifolds include external bypass lines such as the manifolds disclosed in U.S. Pat. No. 5,236,035 to Brisco et al. and U.S. Pat. No. 4,854,383 to Arnold et al., both hereby incorporated herein by reference for all purposes. In more detail, Arnold et al. discloses a conventional external bypass cementing manifold for a single dart or double dart configuration. The single dart manifold comprises a tubular enclosure with a longitudinal passageway into which a dart is loaded. The dart holding/dropping mechanism is a ball valve connected via threads to the bottom of the tubular enclosure. An external bypass line with a bypass valve is connected via welds or threads to the tubular enclosure around the dart. For the double dart configuration, an identical arrangement of tubular enclosure, ball valve, and external bypass line with bypass valve is connected below the first tubular enclosure. Each of the darts in the dual dart configuration is separately releasable.
When the dart is in the hold position, the ball valve remains closed to prevent flow through the tubular enclosure, and flow is routed around the dart through the bypass line by opening the bypass valve. To release the dart, the bypass valve is closed, and the ball valve is opened to allow flow through the tubular enclosure, thereby causing the dart to drop into the well string.
Conventional cementing manifolds often include other external connections, such as the side-mounted sphere dropping mechanisms disclosed in Arnold et al. and U.S. Pat. No. 5,950,724 to Giebeler, hereby incorporated herein by reference for all purposes. In more detail, Arnold et al. discloses a ball dropping mechanism comprising a housing that mounts to the side of thelowermost tubular enclosure. The housing includes a bore in fluid communication with the longitudinal passageway through the tubular enclosure. In the hold position, a ball is positioned on a seat within the housing bore. To drop the ball, a screw shaft pushes the ball through the housing bore and into the longitudinal passageway, thereby dropping the ball down into the well string.
A number of disadvantages are associated with cementing manifolds having external connections, such as external bypass lines and side-mounted sphere dropping mechanisms. In particular, several large penetrations are required in the main body of the manifold (i.e. the tubular enclosures) for making the external connections. These penetrations create high stress concentration areas and hydraulically loaded areas that reduce the overall pressure-containing capacity of the cementing manifold. The manifold must also be capable of withstanding fatigue caused by changes in operating conditions, and stress concentration areas minimize the fatigue life of a cementing manifold. Further, the ball drop mechanism and external bypass connections protrude a considerable distance from the main body of the manifold, making these components more prone to damage during well operations. In addition, the external components connect via threads or welds to the main body of the manifold, thereby presenting a safety concern. In particular, the threads could back out or the welds could fail, which would expose rig personnel to high pressure, high velocity fluids. Thus, it would be advantageous to provide a cementing manifold with internal bypass capability and with few external connections to the main body of the manifold. It would also be advantageous to eliminate threaded or welded connections to the main body of the manifold.
Some cementing manifolds have internal bypass capability, such as the TDH Top Drive Cementing Head offered by Weatherford/Nodeco. The TDH Head is purpose-built for use with a top-drive system and available in configurations to accommodate either a single ball/single dart, or single ball/dual darts. In both configurations, the TDH Head comprises a main body having a main bore and a parallel side bore, with both bores being machined integral to the main body. The darts are loaded into the main bore, and a dart releaser valve is provided below each dart to maintain it in the hold position. The dart releaser valves are side-mounted externally and extend through the main body. A port in the dart releaser valve provides fluid communication between the main bore and the side bore. The ball drop mechanism is externally side-mounted through one wall of the main body below the lowermost dart and extends into the main bore. The ball is retained by a collet, and to drop the ball, a screw shaft pushes the ball out into the main bore.
When circulating prior to cementing, the darts are maintained in the main bore with the dart releaser valves closed. Fluid flows through the side bore and into the main bore below the lowermost dart via the fluid communication port in the dart releaser valve. To release a dart, the dart releaser valve is turned 90 degrees, thereby closing the side bore and opening the main bore through the dart releaser valve. Flow enters the main bore behind the dart, causing it to drop downhole.
Although the TDH Top Drive Cementing Head eliminates external bypass lines, it includes large penetrations in the main body for the dart releaser valves and ball drop device. These external components are also welded or threaded to the main body and protrude a significant distance. Thus, many of the concerns associated with external bypass manifolds have not been eliminated. Further, the parallel flow bores restrict the flow capacity of the TDH unit, which could present erosion problems, and also make it more difficult to remove leftover cement that could clog the bores. Thus, it would be advantageous to provide a cementing manifold with internal bypass capability that does not restrict the flow capacity of the manifold.
The Model LC-2 Plug Dropping Head offered by Baker Oil Tools, a Baker Hughes Company, is an internal bypass cementing manifold for dropping either a dart or a sphere. The LC-2 comprises a mandrel with a releasable dart/sphere holding sleeve disposed therein, the sleeve being held in place by a rotatable lock pin. The sleeve includes ports that allow fluid bypass into an annular area while the sleeve is in the upper locked position. A pivoting stop extends across the bore of the mandrel below the sleeve to maintain the dart/sphere in the hold position.
To drop the dart or sphere, the lock pin is turned 180 degrees to the drop position, which releases the sleeve. The sleeve moves downwardly in response to gravity and fluid flow until it reaches a stop shoulder. The downward movement of the sleeve releases the pivoting stop and restricts flow through the ports leading to the annular bypass area. Thus, the pivoting stop rotates out of the path of the dart or sphere, and all fluid is directed longitudinally through the main bore of the sleeve behind the dart or sphere, causing it to drop down into the drill string.
Although the Model LC-2 Plug Dropping Head eliminates external bypass lines and other external components, the releasable sleeve presents disadvantages. Namely, if the sleeve gets hung up in the mandrel, flow will bypass the dart or sphere, thereby preventing its release. Further, because the lock pin provides only limited engagement with the sleeve, improper assembly or maintenance of the lock pin and sleeve connection could cause the sleeve to release prematurely. Thus, it would be advantageous to provide a cementing manifold with internal bypass capability that does not rely on a releasable sleeve as the dropping mechanism.
In addition to the disadvantages described above, conventional cementing manifolds are typically unitized and purpose-built such that they are not reconfigurable. For example, they can not be converted from a single dart manifold to a double dart manifold and vice versa as the job requires. Further, after the manifold has been used for one job, new darts and/or spheres can not be loaded at the rig site due to the high torques required to disconnect the components to allow reloading. Thus, traditional cementing manifolds must be redressed and reloaded in the shop after each use. In addition, some designs do not enable release of the darts or spheres while pumping fluid downhole due to fluid loads on the release mechanisms. Therefore, known cementing manifolds present various additional operating and maintenance disadvantages.
The present invention overcomes the deficiencies of the prior art.